A silver layer provides neutral transmitted color and reflected color in the visible region and has a low resistivity. A silver layer having a geometrical thickness at a level of 10 nm has little absorption in the visible region and has a reflectance of several tens %. The reflectance increases as the wavelength becomes long, and in the infrared region, it has a high reflectance. A silver multilayer film comprising a silver layer sandwiched between dielectric layers, having a low reflectance in the visible region and a high reflectance in the infrared region, has an outer appearance equal to that of common glass, and has a low emissivity and a high heat ray reflectance, and accordingly it has been used for highly heat insulating Low-E glass or heat ray-reflective glass having a high transmittance. In recent years, along with an increase in the energy saving consciousness, demands for such glass are increasing. Further, since it has a low resistivity, it may be used as a transparent electrically conductive film.
Tempered glass is sometimes used as Low-E glass, for example, window glass for a building. Further, curved glass is used as window glass for an automobile. Both tempered glass and curved glass are produced by a heat treatment at a temperature of from 550° C. to 750° C. There are two methods for producing tempered glass or curved glass having a silver multilayer film. A first method is a method of forming a film on glass which has been tempered or curved. A second method is a method of forming a film on a large-sized flat glass, cutting the glass into a glass plate of a product size, and subjecting the glass to a heat treatment for tempering or curving.
The production cost is lower in the above second method of forming a film first and then cutting the glass and subjecting it to a heat treatment for tempering or curving, than a method of forming a film on glass which has been tempered or curved. It is difficult to stably produce a high performance silver multilayer film with substantially no deterioration after the heat treatment, and various know-how is required. As glass having a silver multilayer film and having the haze or the like at the time of the heat treatment suppressed, one having a NiCrOx film formed to sandwich a silver layer has been known (for example, Patent Document 1).
Further, as Low-E glass or the like, one comprising a light-absorbing layer in combination with a silver layer, in order to decrease the transmittance and to improve heat ray-shielding properties, has been known. One comprising a light-absorbing layer in combination with a silver layer may, for example, be one having a light-absorbing layer directly over a silver layer (for example, Patent Document 2 or 3).